Multicasting is a method for simultaneously delivering data over a network from one or more data sources to a number of data receivers. Multicasting systems employ routing protocols to link the data sources to the appropriate data receivers in an efficient manner.
Multicasting networks are provided by multicast enabled nodes within or connected to an existing network. The nodes comprise multicast sources, multicast receivers and multicast routers. The multicast sources are the source of the multicast data that is carried via the network to the multicast receivers. The multicast routers are arranged to route the multicast data packets across the network between the multicast sources and receivers.
Two tasks are performed for the implementation of a multicast network. Firstly, the membership of a set of receivers needs to be managed. This group management may be performed manually by network administrators. Alternatively, a multicasting group management protocol may be implemented on network nodes that connect receivers, to enable the automatic management of the joining receivers to a multicast group. An example of a group management protocol is the Internet Group Management Protocol (IGMP).
Secondly, the routing of the multicast data over the network is managed. Such routing may be configured manually by network administrators. Alternatively, a multicasting routing protocol may be implemented on each node in the network to enable the automatic creation of multicast distribution trees, such as a tree information base (TIB), between the multicast sources and receivers. Examples of such routing protocols include Protocol Independent Multicast (PIM) protocols. The IGMP and PIM protocols are implemented generally in accordance with standards defined by the Internet Engineering Task Force (IETF).
One of the difficulties of debugging multicast traffic is determining the health of a multicast flow. Reports of issues in the network are typically receiver-driven whereas the fault itself can be at a considerable distance from where the symptoms are felt.